Reversal of left bundle and His bundle potentials during wide complex tachycardia: What is the mechanism?

Abstract

Case presentation A 14-year-old male patient presented to our institution with a wide complex tachycardia. An echocardiogram showed an ejection fraction of 60%, moderate mitral and tricuspid regurgitation, mild aortic regurgitation, and moderate pulmonary hypertension. He had a history of 2 prior ablations at another institution. During his first procedure, he was found to have ventricular tachycardia with a right bundle branch block, left superior axis morphology at a cycle length of 375 ms. Cryoablation was performed along the mid-left ventricular septum, after which the patient developed a left posterior fascicular block pattern during sinus rhythm. The next day, the patient developed ventricular tachycardia with a right bundle branch block, right inferior axis morphology. Ablation was targeted in the region of the left anterior fascicle and rendered the tachycardia noninducible. After the procedure, the electrocardiogram demonstrated a left bundle branch block configuration. Several months later, the patient presented to our institution in a wide complex tachycardia with a left bundle branch block, left superior axis morphology. Electrocardiograms during sinus rhythm and tachycardia are shown (Figures 1A and 1B). During electrophysiological study, baseline AH and HV intervals were 87 ms and 55 ms, respectively. The HV remained constant during incremental atrial pacing. Tachycardia was reproducibly induced with rapid atrial and ventricular pacing, and had a cycle length of 370 ms and an HV interval of 55 ms. Atrial activity was dissociated from the tachycardia. Adenosine 24 mg had no effect on tachycardia cycle length. Intracardiac tracings during sinus rhythm (Figure 2) and tachycardia (Figure 3) are shown. What is the mechanism of the wide complex tachycardia?